Ghost people are mutated humans changed forever by the Cloud, a combination of corrosive rust-like toxins unique to the Sierra Madre. A green vapor that seems to be a byproduct of the Cloud escapes and is reabsorbed continuously from their hazmat suits by means of aeration on their thighs, elbows and face mask, indicating that their mutation originates from permanent exposure to the Cloud. They are the only ones able to walk in and out of the Cloud unharmed.
The ghost people originate from construction workers that worked on the Sierra Madre Villa before the War. During construction, a strange gas that would evolve into the Cloud began leaking from the pipes and hospitalized a worker with severe lung and tissue damage; further progress was called off until protective gear could be issued. Hazmat suits designed specially in Big MT arrived to protect against the noxious gas. Incidentally, the gas leak itself was also created at Big MT, and with the hazmat suits being an "experiment within an experiment." The hazmat suits were bulky, nearly impossible to speak through, and grew stiff with use. The locking mechanisms would quickly corrode when in contact with the Cloud, to the point where the hazmat suit had to be cut open with a cosmic knife, yet the suits still didn't provide proper protection from the poisonous gas cloud.
Ghost people are similar to feral ghouls in several aspects. Dismembering them reveals bright, glowing blood, akin to that of a glowing one and they also shriek before attacking. However, they seem to be a different mutated evolution and not simply a feral ghoul or glowing one in appearance, as their ability to use and construct weapons is still intact. Virtual immortality and death only with limb amputation is also a mutation very specific to them.
The moniker "ghost people" can also be ascribed to the ghostly manner in which they inhabit the ruins; their manner, movements and general presence are seemingly much akin to a malignant haunting to any who have survived and fled attempts to breach the Sierra Madre. Dean Domino questions whether being "alive" applies to the ghost people, and claims there are hordes and hordes of ghost people living under the Sierra Madre's streets, comparing it to a hornet's nest. It is not clear why the ghost people drag their victims off into the Cloud. Whether to consume, torture or convert them into something like themselves nobody knows, or has survived to tell the tale.
Ghost people are mysterious creatures; they do not speak, and they never sleep. They seemingly exist only to lurk through the villa ruins, forever seeking prey. If they have a lair at all, it is unclear where: according to Dean Domino, they collect anywhere in the Sierra Madre away from holograms; the underground service routes and ruined buildings of the Sierra Madre Villa are prime habitats for them. Their most common hunting grounds are Salida and Puesta del Sol, especially in areas thick with the Cloud.
The centuries-old stiffening hazmat suits and Cloud-related malady force them to shamble like undead creatures. Despite this, they are in fact quite agile when necessary, often lunging and dashing at high speed. The ghost people are incredibly territorial (and equally hostile) and oust any intruder in the Sierra Madre. Their primitive minds still form some semblance of group tactics; they hunt their prey similarly to a pack of wolves. They band together in groups of two to three and hide in the refuges of shadow and Cloud, striking relentlessly when prey wanders too close.
Ghost people enjoy apparent immortality, but possess a unique mutation whereby they only die if one of their limbs is dismembered. Blood and yellow fluid spray at high pressures when they are injured, which Dog explains as them having pockets of pressurized gas inside them.
All ghost people are hostile to the Courier. They are difficult to pin down, as they will constantly lurch and jump around during engagements. They also actively avoid a rifleman's aim, particularly near their head. They do not utilize firearms, using only primitive weapons made from resources found in the Sierra Madre villa. Ghost people can be more difficult to kill with firearms than most other opponents because they do not take extra damage from headshots. This is somewhat balanced by their complete lack of functioning armor.
They are difficult to kill permanently by normal means; they must be disintegrated, dismembered or eaten by Dog, or they will simply get up and continue attacking. The simplest way to keep them from getting back up is to cripple or dismember their limbs with a melee weapon (like a cosmic knife,) an explosive (like a demolition charge,) or from concentrated ranged attacks to a single limb. The loss of a limb will always kill the ghost person. If a ghost person is already down, attack with a melee weapon or target their limbs with a ranged weapon until a limb is removed to stop them from reviving. Crippling a limb while a ghost person is conscious will dismember the limb, killing them even if the crippling attack does not reduce their health to 0. The Bloody Mess perk helps considerably with this task, since it increases the chance of dismemberment with standard firearms. The revival of the ghost people is indicated by characteristic gurgling, so it is recommended to either stand back or quickly destroy one of their limbs before they wake up.
However, after a certain dialogue path with Dog starting with the phrase "I watched you devour one of the ghost people," Dog will give the Courier the Ghost Hunter perk, allowing one to kill ghost people without Dog or chopping off their limbs.
Often the only warning of their presence is a strangled choking or muttering sound they make. Ghost people are technically exceedingly easy to sneak by, as they have zero Perception, but the narrow streets and many traps around the Villa make sneaking past them much harder.
Ghost harvesters are the most common variant of ghost people. They are the smallest variant and are easily distinguished by their hoods and smaller gas masks.
They are equipped with knife spears and throwing knife spears, using the throwing spears until they are exhausted and then charging the target equipped with a knife spear, unless the prey closes to melee range first.
They are not the most durable or proficient opponent in close combat, but their throwing knife spears can cause great damage in a short time. Also, they usually perform a jump to the right or left after throwing a spear, which makes them hard to target with a firearm outside of VATS.
“Where there's a bear trap, Ghost People aren't far behind.”— Dean Domino
Ghost trappers can be identified by their large size and lack of hoods. They are only equipped with bear trap fists. Ghost trappers are also responsible for the inordinate amount of bear traps and trip wires in the Sierra Madre.
They are capable and tough unarmed fighters, so they are best picked off from a distance. However, ghost trappers are often found in groups with knife spear-bearing Harvesters or Seekers.
Ghost people will not set off tripwire-based traps.
It is possible, while in Sneak mode, to see ghost trappers resting with one knee on the floor and holding a Knife spear as support, even though they don't use knife spears or have any on them upon death.
If summoned using commands, ghost people will only be hostile to the Courier and their companions, and only the Courier's companions will be hostile to them. Other NPCs, however, will still say lines such as "Watch out!"
They seem to be responsible for some of the graffiti seen throughout the Villa, as a Seeker can be observed nailing boards to a gate connecting Salida del Sol North and South, and on the North side the word "escape" crossed out can be seen.
↑Villa clinic terminals; Terminal, Gas Leak: "Admitted 3 workers from Puesta del Sol Switching Station. Exposed to some unidentified airborne toxin from the ventilation system. Caused severe lung and tissue damage, inhalation isn't the problem, it's absorbed through the skin."
↑The Courier: "Is anyone else alive around here?" Dean Domino ""Alive's" a tricky word. The locals, the Ghost People? Not sure it applies to them. They're a little... uncivilized. They don't talk much. As in, at all." (Dean Domino's dialogue)
↑The Courier: "Is there anything else about them I should know?" Dean Domino: "Whatever we do - don't rile them up. Normally, there's only a few, maybe a pack. There's more out there, a lot more. If they find out someone's trespassing, it'd be shaking a hornet's nest. Don't want to think how many of them could fill these streets." (Dean Domino's dialogue)
↑A skeleton and embalming fluid near the Villa bell tower support this theory, although it could simply be embalming fluid from before the War.
↑Dean Domino: "Was that him floating above the Fountain, the boss man? The one who put these bowties on our necks?Sure does like to make a presentation... wish he'd keep it down, or else the Ghost People are going to swarm the gates, Vera Hologram or no." (Dean Domino's dialogue)
↑The Courier: "If I clear out all the Ghost People in the area, will you change your mind?" Dean Domino: "No, you want to know why? Because there's more beneath the streets, in the buildings, and oh - everywhere else. They hear anything out of the ordinary, especially "music" screaming through the speakers when I close the connection? They'll be here, fast." (Dean Domino's dialogue)
↑The Courier: "What can you tell me about the Villa and the town?" Dean Domino: "Residential area, clinic, police station - should keep away from the police station, it's a Ghost People hangout. Salida del Sol, Puesta del Sol are East Town, West Town. "Sunrise" and "Sunset." Or were when the streets and sky weren't covered with toxic gas. Ghost People don't come into the Villa much. West Town and East Town, though... they're thick with the Cloud and Ghost People. Like hunting grounds." (Dean Domino's dialogue)
↑The Courier: "How tough are they?" Dean Domino: "You shoot them, they get back up. You stab them, they get back up. That's why I have explosives all over this place - unless you blow them up, chop them up, disintegrate 'em, the Ghost People don't go down. Not enough bullets in the town to spend on them. So unless you're a real good shot, save one for yourself right before they catch you." (Dean Domino's dialogue)
↑The Courier: "Do you know how the Ghost People taste?" Dog: "Taste like plastic and copper. Gas inside, in pockets, hssss when teeth sinks into them." (Dog and God's dialogue)